The present invention relates to the use of substituted thioureas for the separation of complexly bound heavy-metal ions from reaction solutions and waste water containing inorganic and/or organic complexing agents such as ammonia, amines, diamines, amino acids or hydroxy acids.
Due to their toxicity, heavy metals must be separated from waste water and reaction solutions down to residual concentrations of a few milligrams per liter. This normally occurs by means of neutralization with sodium hydroxide solution, soda or milk of lime. Slightly soluble metal hydroxides or metal carbonates form thereby which can be removed by sedimentation or filtration. If complexing agents are present in the solutions, this method fails. Here in the latter instance, other techniques are used such as overalkalization, electrolysis, metal-sulfide precipitation with hydrogen sulfide or the use of trimercapto-S-triazine-trisodium salt solution (TMT 15).
These methods have the disadvantage that they are in part very complicated and expensive, do not achieve high depletion rates or do not result in certain areas of utilization in readily filterable precipitates.
DE-PS No. 33 40 056 corresponding to U.S. Pat. No. 4,571,265, teaches a method for the separation and purification of platinum metals from the other noble and base metals from acidic solutions in which method substituted thioureas of the general formula R.sub.1 R.sub.2 N-CS-NH-COR.sub.3 are used. However, these solutions do not contain complexing agents.